The invention relates to a method and a device for the determination of a vertical acceleration of a wheel of a vehicle for the use in vehicle dynamics control or monitoring, which can be operated in a cost-saving manner, in particular by means of the sensory detection of only a few auxiliary quantities.
Many modern vehicle control systems and vehicle monitoring systems, respectively, which influence or monitor the horizontal or vertical vehicle dynamics, require among others the dynamic normal wheel forces as input quantities. The normal forces are those forces that act upon the wheels through the tire print on the road surface. The dynamic normal wheel forces, however, can only be determined with a significant expenditure, which is the reason for currently making simplifications in applications. However, by this means, the control quality of the control systems is significantly compromised.
Several methods for the determination of the dynamic normal wheel forces are known. In order to determine the dynamic normal forces of the wheel during driving operation, direct measuring methods with multiple-component measuring hubs (see e.g. SAE 980262 xe2x80x9cEvaluation of Different Designs of Wheel Force Transducersxe2x80x9d) are ruled out due to the high costs for these sensors. In indirect methods, auxiliary quantities are measured, from which the dynamic normal wheel forces can be computed. For the production suitability of these methods, therefore, the expenditure for detection of these auxiliary quantities is crucial. The Braunschweig method, the Munich method, and the tire-inside-pressure method use the tire as a measuring spring, wherein the dynamic normal wheel force is computed via a characteristic curve from the vertical tire spring compression, the lateral tire expansion, or the tire inside pressure, respectively (see e.g. Gersbach et al.: xe2x80x9cComparison of Procedure to the Measurement of Wheel Load Variations, ATZ Periodical Technical Automobile 80, 1978; Bode: xe2x80x9cComparison more Differently Proceed to the Determination of the Dynamic Wheels Loadxe2x80x9d, German on the Basis of Research Goes and Strove Associate Technology, No. 131, VDI-publishing house, 1959). The measurement of these quantities and the necessary telemetry are very elaborate. Additionally, the required characteristical tire curves are subject to great variations. The Hanover method (Bode, noted above) and the Darmstadt method (Svenson: Investigations of the dynamic krafte between wheel and street and its effects on the stress of the street, No. 130, VDI-publishing house, 1959) use expansion measuring strips in order to make conclusions on the dynamic normal wheel force through the expansion of the axle body or the hub bed, respectively. A method based on expansion strips is not suitable for production, either, due to the high cost and the elaborate calibration.
Significantly more common are, due to their comparably easily measurable auxiliary quantities, the Aachen method (Kotitschke: The dynamic wheels weight of motor vehicles; its measurement and its influential factors, RWTH Aachen, 1957) and the intersecting-forces method (Tiemann: xe2x80x9cInvestigations to the brake behavior of automobile with ABS on uneven street under special consideration of the influence of the oscillation mute, progress-reports VDI Row 12 nr.s 204, VDI-publishing house, 1994). In the Aachen method, the normal wheel force Fz is computed from the proportionate vertical acceleration {umlaut over (z)}B,V, in the following text called partial vertical body acceleration, the proportionate mass of the vehicle body (quarter vehicle) mB,V, and the vertical wheel acceleration {umlaut over (z)}W with the proportionate wheel mass of a wheel mWz (see FIG. 1):
Fz=mB,Vxc2x7{umlaut over (z)}B,V+mWzxc2x7{umlaut over (z)}Wxe2x80x83xe2x80x83(1)
The intersecting-forces method evaluates the spring stroke Dz of a spring 2 and the vertical wheel acceleration {umlaut over (z)}W for the determination of the dynamic normal wheel force Fz (see FIG. 1):
Fz=cBzxc2x7xcex94z+dBzxc2x7xcex94{dot over (z)}+mWzxc2x7{umlaut over (z)}Wxe2x80x83xe2x80x83(2)
Both methods require the vertical wheel acceleration {umlaut over (z)}w. Accelerometers for the measurement of this quantity, however, are expensive due to the high accelerations occurring at the wheel and to the extreme environmental influences.
It is an object of the invention to identify, for the use in driving dynamics control, a method and a device for the determination of a vertical acceleration of a wheel of a vehicle that is simple and cost-effective to realize.
This objective is achieved with the features of the independent claims. Dependent claims are directed to preferred embodiments of the invention.
According to the invention, a first determination device can determine a spring acceleration of a spring which is mounted between the body and the wheel and loaded in the vertical direction by the vehicle body. A second determination device can determine a partial vertical body acceleration. A control unit can further determine a vertical acceleration of a wheel (vertical wheel acceleration) by adding the spring stroke acceleration from the first determination unit and the partial vertical body acceleration from the second determination unit. The thus determined vertical wheel acceleration can then be used e.g. for the determination of the normal wheel force. In this invention, an expensive sensor arrangement for the detection of the vertical wheel acceleration can therefore be eliminated, and the results of the determination of the vertical wheel acceleration according to the invention reflect very accurately the actual comparison test results.
Various embodiments of the invention are now exemplarily explained with respect to the attached schematic drawings. Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawing.